kc_avis
I was on the cadet program with CX.
First of all to get into the ab-initio program without any experience you'll need to be a HK permanent resident, if you're not then you can still get in but only onto the 'advanced' program where the requirements are 250hrs and a CPL although apparently they don't really take people with experience that low.
The basic entry requirements are pretty low (I think you only needed the equivalent of 2 A levels to apply) however, everyone on my batch had at least a bachelor degree and I don't know of anyone that was hired straight out of high school. I think while not a hard requirement CX definitely prefers those with a degree and also the maturity that a candidate will have being a bit older as well.
The selection process is tough and as it is open to anyone (with a HKID) without any financial obligations the competition is pretty tough. From my experience in the interview they won't ask you any crazy technical questions although they will try and push you until there are things you don't know and will try and see your response to that. The questions can get pretty tough and up to ATPL level so actually might be similar to those that you've found. If the process is still the same they will send you an FAA book (pilots handbook of aeronautical knowledge) which will set you up well for the technical test in your stage 1.
If you are in HK then I would definitely suggest going to university in a STEM subject, aero engineering might be interesting to you although choose something that you enjoy as it will look much better if you finish than if you do something and then give up halfway because its something you 'thought' you should do. Also study up on the FAA book, its fairly long and should keep you studying for a while especially if the concepts are new. Also definitely worth going to australia or NZ when you can and trying to get at least to first solo stage - shows passion and also whether you'll actually like flying.